Sound transmitter



Jan. 23, 1945. s. F. LYBARGER SOUND TRANSMITTER NMA Illllllllllll lul/.f ATTORNEY@ be considered satisfactory.

Patented Jaa. 23, 1945 UNITED STATE? assises PATENT OFFICE SOUND TRANSMITTER Samuel F. Lybarger, Pittsburgh, Pa., assigner to E. A. Myers & Sons, Pittsburgh, Pa., a partnership consisting of Edward A.- Myers, Edwin J. Myers, Alfred E. Pelz, and Samuel F. Lybarger Applicatioalanuay 10. 1942, serai No. 426,343

s claims. (c1. 11n-.32)

lar-electrically responsive crystals for converting the'electric power supplied to them into acoustic energy which is delivered to the ear oi the wearer.

Most hearing aid crystal receivers employ a long narrow crystal which extends nearly across the receiver case and has its opposite ends anchored and its central portion connected to the diaphragm and free to vibrate in response to the electric power supplied to it. Such a crystal -has a length nearly as great as the width of the case. While a bender .crystal of the typev commonly used gives a relatively high eillciency up to about 3500 cycles, the number'ofiailuges of such crystais in service has been so high that they can not- Besides, .the frequency curveoi such a crystal shows non-uniformities which are not desirable and does not extend to a sufiicientlyhigh frequency with good etlicien-cy. Moreover, such a "bender crystal has to be extremely thin and comparatively long in relation to its width in order to attain sufiicient exibility to give the desired frequency response characteristics. A The actual crystal thiclness is generally .020 inch, which means that each section of the crystal is only .010 inch thick. The mechanical diiculties involved in handling such long thin slabs of Rochelle salts are considerable. They are subject to mechanical breakage because of their relativelyI long length, and are also affected by humidity very much more than the more compact square type that will be referred.

Another disadvantage of a long,

to presently.

narrowfcrystal is that itis supported in the .case

at only two widely spaced points.

i more practical type of crystal is a square one plied to the crystal will cause it to tend to twist and thereby cause its free corner to vibrate. 'I'his type of crystal is quite sensitive and the amount oi motion secured is-relatively large in comparison with many other arrangements. However, the principal objection to twister crystals has been that in order to use such a crystal of a practical size the case must be relatively large because the free corner oi the crystal is located at sub.

stantially the center i the case below or behind the center of the diaphragm. lin attempt has been made to use a smaller case, without reducsmaller case with an offset in which a portion o! the crystal is housed. With such an arrangement .a crystal may be employed whose edge is nearly one-half the length ofthe inside diameter of the case. -Nevertheless, there is a definite objection to the increase in size of the receiver necessitated by the ofl'set, and the amplitude of vibration of '-the.diaphragm can not exceed that of the free corner of the crystal.

A problem that arises with all crystal receivers is that of service and repair. They are so diiiicult to repair that the practice is to discard the entire receiver and replace it with a new one.

It is among the objects of this'lnvention to pro-l vide a crystal receiver which `has greatly improved eiliciency for its size, which has more uniform and wider frequencyv response characteristics than heretofore, which'is rgged in construction, which utilizes a type ofcrystal that is mechan- 2 icallystrong and affected by humidity to the least possible degree, which is simple in construction and easy to assemble, in which a much larger proportion of the available space inside of thereceiver case is occupied by the crystal to thereby permit the use of a larger crystal giving greater sensitivity, in which the' sound reproducing unit isa separate element which can be easily replaced by a dealer or user without replacing thezentire receiver case, in which means may be. provided for damping the vibration of the reprodubing unit so that practically al1. of the vibration is that of the `diaphragm whereby back radiation from the receiver case is reduced to the point where it does not feed-back to the microphone of the audi- '35 phone, and in'which a denitelever action is present so that the relatively high mechanical impedance of the crystal itself is emciently matched to the considerably lower impedance of the diaphragm and air column beyond. j

r 4o The invention is illustrated in the accompanyso constructed that when three of its corners are. more or less anchored the electric voltage suping drawing in which Fig. 1 is a greatly enlarged bottom plan view of my receiver as shown herein; Fig. 2 is a transverse section taken on the line II-II of Fig. 1; Fig. 3 is a transverse section taken on the line III- III of Fig. 2; Fig. 4 is a Fig. 6 is a view similar to Fig. 5 of a modiiication of this invention; Fig. 7 is a reduced plan view of Fig. 6 broken away in part; Fig. 8 is a plan view similar to Fig. 7 of a further modification of this invention; Fig. 9 is a sectional view simiing the size or the crystal, by providing the u lar to Figs. 5 and 6 of the modification shown in- Fig. 8; and Figs. 10 and 11 are fragmentary plan views of additional modifications of my invention.

Referring to Figs. l vto 4 of the drawing, an audphone receiver case is formed from a cupllke base member I of Bakelite or the like and a metal cover 2 screwed on the base. The cover is provided with acentral opening 3 encircled by an integral boss 4 adapted to receive an ear tip (not shown). for holding the receiver in the ear of a person who is hard of hearing. f

In accordancce 'with this invention the reproducing elements of the receiver are not connected directly to the case as has been the practice heretofore. but they are mounted in a metal cup S that is removably mounted in the case and held therein only by the cover so that if any repairs are required the reproducing elements can be readily removed as a unit and a new unit quiclrly inserted in their place. The cup preferably is cylindrical with a flat bottom and with an open top encircled by an integral flange 'l on which rests the marginal portion of a diaphragm Il of metal or other suitable material.

Disposed within the cup below the diaphragm is a square piezo-electric crystal 9 having three corners secured to slightly resilient triangular pads I ailixed to the bottom of the cup close to its side wall. The fourth corner is therefore left free to vibrate when the crystal is supplied with varying electric voltage through wires II connected to a pair of metal terminals I2 attached to rivets I3 extending through the bottom of the cup on opposite sides of the free corner of the crystal. 'I'he rivets are insulated from the cup by encircling insulating headed sleeves I4 and by an insulating blockl I5 held against the outer surface of the cups bottom by the rivets, as shown in Fig. 3. These rivets clamp against the insulating blocka pair of tubular spring clips I1 for receiving and gripping the tips of wires (not shown) from the microphone with which the receiver is used. The bottom of the case has a thick central portion provided with a pair of parallel passages I8 through which the microphone wires are led to the clips. When varying electric voltage is supplied to the crystal from the microphone, the tendency of the crystal lto twist causes its free corner to vibrate and this vibration is transmitted to the diaphragm through a driving pin I9 secured thereto and hooked around the free corner of the crystal to which it is cemented.

The cup 8 is clamped in the case by the cover 2 from which the diaphragm is spaced by a disclike cap 2i provided with a marginal portion resting on the marginal portion of the diaphragm as shown in Figs. 2 and 3. The cap is encircled by a flange 4I that overlaps flange 1 of the base member to center the cap. The major portion of the cap is pressed outwardly toward cover 2 so that none of the diaphragm that does not touch flange 'I is touched by the cap either. The cap preferably is slightly convex so that when the cover is screwed onto the base member it iirstl engages the center of the cap and then presses it inwardly, thereby insuring tight engagement bel tween cap and cover'to prevent the cap from vibrating. The center of the cap is provided with a few small holes 42 in line with opening 3 in the cover. The cap is cemented or otherwise attached 'to the cup 6 and thus prevents the dell-v vibration of the bottom of the cup from vibrating the bottom of base I and thereby feeding sound back to the microphone, the bottom of the cup is spaced from base I, and its vibrations may 'oe damped by resilient pads 22 of felt, sponge rubber or the like mounted in the base in engagement with the bottom of the cup, asshown in Fig. 2. The side wall of the case-is the point of least vibration-of the case and it is to that point that the cup is clamped by its flange l. This feature also helps lprevent the cup from vibrating the case. When the receiver requires repair work it is a simple matter to merely unscrew cover 2, remove cup 6, insert a new cup in its place, and replace the cover without discarding the entire receiver.

Another feature of this invention is that the crystal is connected to the diaphragm in such a manner that a much larger square crystal can be used than heretofore for the same size case. This results in a stronger crystal than the customary oblong bender crystal, one easier to handle, and-a crystal .that is affected less by humidity. These advantages are obtained by using a substantially square crystal which is nearly as far across diagonally as the inside of the case, Wherev by the free corner of the crystal is disposed lat erally of thecenter or axis of the diaphragm, and by connecting that corner of the crystal to the diaphragm oil center of the latter, or to its center through the medium of a lever. When driven off center, the diaphragm preferably has a substantially stifcentral portion to which the driving pin is connected. Most suitably, as shown in Figs. 2, 3 and 4, the central portion of the diaphragm is made stiil byproviding it with a depression, preferably conical with the base of the cone either circular or elliptical (Fig. 4) and with the apex off center and nearly above the free corner of the crystal to which it is connected by pin I9. The stii cone carries the vibrations of the crystal throughout the area of the diaphragm. If the stiff portion of the diaphragm is anything but round, it is preferred that its long axis extend in the direction of the crystal diagonal that passes through the driving corner. The driving pin preferably is flexible laterally so that it can yield and not cause the far side of the diaphragm cone to tilt down into the cup when the free corner of the crystal swings upwardly.

The amplitude of vibration of the free corner of the crystal can be increased by using a diamond-shape crystal so that its two opposite anchored corners can be located closer to the side of the case, or, as shown in Fig. 10, by attaching rigid metal extensions 23 to those two corners of the crystal and mounting their outer ends on pads I0 at the side of the case; This, in ei.'- fect, increases the length of one diagonal of the crystal so that its center can vibrate through a longer path for the same amount of bending.

A further important feature of this invention is that the amplitude of vibration of the major portion of the diaphragm can be increased over that of the vibrating free corner of the crystal. This may be accomplished in several ways, all of which make use of leverage. Thus, the at area of the diaphragm surrounding the cone may be made with varying degrees of stiffness or resil iency, the resiliency being least in the area between the periphery of the diaphragm and the cone edge closest to it, which is at the left of the driving pin as seen in Figs. 3, 4 and 5. In such a case the resiliency or stiffness is so controlled that the total effective stiiness of the ilatarea of the diaphragm lying between a line .Ii-A, shown in Fig. 4 extending across the diaphragm directly above the driving pin and perpendicular to the major axis of the cones base, and the adjacent side of the cup is greater than the total effective stiffness of the remaining flat area of the diaphragm. It is important that the total stiffness of the diaphragm presented to the vibrating corner of the crystal be kept relatively low in order to prevent loss of amplitude at low frequencies. Due to the stiffness control, as shown in Fig. 5, the amplitude of vibration of the fiat area at the left of the driving pin is constrained relative to the remaining flat area of the diaphragm to such an extent that it serves as a fulcrum for theI adjacent end of the rigid conical portion which thereby acts as a lever and causes the major portion of the diaphragm to vibrate with a greater amplitude than the apex `of its conical portion. As driving pin I9 will yield laterally, it does not interfere with this canting movement of the diaphragm. Or the yielding of theV apex of the cone will serve the same purpose.

In the modification of` the invention illustrated by Figs. 6 and 7 the same large twister" type of crystal is used as in the first embodiment, and its free or vibrating corner is connected by a, resilient driving pin 26 to the diaphragm 21 near the side of the metal cup 28 in which these elements are housed. However, the

, cone that makes the central portion of the diaphragm stiff may have a circular base nearlyas large as the diaphragm, but preferably eccentrictherewith. The major portion of the periphery of the diaphragm is spaced from the side wall of cup 28, but is connected thereto by a; very flexible ring 28 of oiled silk or other impervious material. The inner edge of the ring is cemented to the lnarrow'flat marginal area of the diaphragm, and

its. outer edge rests on Ntop of the metal cup. When the diaphragm is vibrated by the crystal it vibrates substantially as a rigid unit, the vibration being permitted by the encircling resilient ring 29.

Although the desired lever action that i n.

. creases the amplitude -of vibration of the dia phragm over that of the crystal is obtained to some extent if the diaphragm is entirely free of the cup, the diaphragm can be provided in the area closest to the driving pin withv a laterally projecting integral tab or ear 30 the outer end of which rests on top of the cup. This tabpbeing made of the thin material of the diaphragm, has some resiliency, but mucl'i less than the silk ring. Consequently, the tab tends to restrain vibration of the adjoining side of the diaphragm is vconnected to the center of the diaphragm through the medium of a lever 31. The central portion of the diaphragm is made substantially rigid by providing. it with 4a conical depression having a circular base concentric with the diaphragm and having its apex at the center of the diaphragm. The fiat area of the diaphragm encircling its cone flexes `when the diaphragm is vibrated, as shown in Fig. 9. The lever by which the driving pin is connected to the center ci' the diaphragm may take various forms. The vone illustrated in Figs. 8 and 9 is in the form of a approximate only.

tiny stiff bar the outer end of which is bent at substantially a right angle and rigidly connected vto the side of the cup 38 by a fastener 39. The

portion of the lever between the case and its radially extending portion will twist sufficiently to permit the inner end of the lever to vibrate axially of the case. The inner end of the lever is cemented to the apex of the diaphragms cone, and driving pin 36 is attached to the lever between its ends. When' the free corner of the crystal vibrates, the driving pin causes the lever to vibrate which in turn vibrates'the diaphragm. It will be seen that. due to the crystal being connected to the lever between its ends, the inner end of the lever will vibrate in allonger arc than the free corner of the crystal, and therefore the amplitude of vibration of the diaphragm is' greater than that of the crystal. Although this invention has been 'described in connection with a receiver, it will be understood that the same general principles can be used in a microphone to advantage.

To permit a better understanding of the invention I shall now give some of the approximate dimensions of a. receiver, constructed in accordance with this invention and which has proved to be very satisfactory. l Of course, these dimensions are not the only ones that might'be used. but are given merely by way of example and are The overall diameter of the cup 6 is 3A inch and its inside diameter' 4%4 inch. The diaphragm is made from aluminum rfoil .001 inch thick, and the apex of its conical portion is 3/4 inch below the top of the diaphragm. The conical portion hasv an elliptical base and an eccentric apex formed by pressing the diaphragm with a die made by cutting off at an oblique angle a tool having the shape of a right cone.'

f The major and minor axes of the elliptical base and thus serves as a fulcrum or hinge on which the rest of the diaphragm swings. The result is that the major portion of the diaphragm swings or vibrates with a greater amplitude than the apex of its cone which is connected to the driving' pin 26.

If ear 30 is not used, a'tinyweight 3l can be mounted on the .edge portion of the diaphragm at the same point, as shownin Fig. 11. l The inertia of this weight constrains vibration of the adjoining area of the diaphragm and thereby causes the opposite side of the diaphragm to vibrate in a greater arc. The weight therefore serves, in effect, as a fulcrum for the diaphragm.

In the modication shown in Figs. 8 and 9 the large twister.crystal 35 has its vibrating corner near the side Wall of the cup as previously explained, but the driving pin 36, instead of beingv of the conical portion are and inch, respectively. The shortest distance between the apex and a line passing through the edge of the base of the conical portion of the diaphragm is 1 inch, while the longest distance is inch.

The narrowest width vof the fiat portion of the diaphragm surrounding the conical portion is 1;/8 inch, and the greatest width is inch.

According to the provisions of. the patent* statutes, I have lexplained the principle and construction of my invention and have illustrated and. described what I now consider to represent its best embodiment. However, I desire to have it understood that.'y within the scope of the appended. claims, the invention may be practiced otherwise than as specifically illustrated and described. i

I claim:

1. A sound transmitting vvibratable integral diaphragm of substantially uniform thickness throughout its area for use in a case containing a piezo-electric crystal. said diaphragm having an eccentrically .positioned'depression the wall oi' which tapers toward a driving point, said wall forming a stiiening portion in the diaphragm surrounded by a flexible substantially flat area, said driving point being located between the center of the diaphragm and the narrow pari; of said ilexible area and adapted to be operatively connected to a piezo-electric crystal, and the outer edge of said ilexible area being adapted to be held substantially stationary when the rest of the diaphragm vibrates, whereby during vibration of the diaphragm the wide part of said ilexible area opposite said narrow part has a greater amplitude of vibration than said narrow part.

2. A sound transmitting vibratable ,diaphragm for use in a case containing a piezo-electric crystal, said diaphragm having an eccentrically positioned stiiened portion provided with a wall of substantially uniform thickness and surrounded by a flexible substantially at area the outer edge of which is adapted tobe held substantially stationary while the rest of the diaphragm vibrates, and said stiiened portion having a driving point located between the center of the diaphragm and the narrow partfof said exible area and adapted to be operatively connected to a piezo-electric crystal. whereby during vibration of the diaphragm the wide part of said flexible area opposite said narrow part has a greater amplitude of vibration than said narrow part. l 3. A sound transmitting vibratable diaphragm for use in a case containing a piezo-electric crystal, said diaphragm comprising a relatively stiff` member, a resilient tab projecting laterallytherefrom, and a flexible sealing member surrounding said stiff member and secured thereto, the outer vedge of said sealing member and the outer end of said' tab beingV adapted to be held substantially stationary while the rest of the diaphragm vibrates, and said stiff member having a driving point located between the center of the diaphragm and said tab and adapted to be operatively connected to a. piezo-electric crystal, whereby during vibration of the diaphragm the part of said sealing member opposite said tab has a greater amplitude of vibration thanr saidl tab.

4. A sound transmitting vibratable diaphragm for use in a case containing a piezo-electric'crystal, said diaphragm comprising a relatively stiff member, a flexible sealing member surrounding said stiff member and secured to the edge thereof,'the outer edge of said sealing member being adapted to be held substantially stationary while the rest of the diaphragm vibrates, and a weight attached to one of said members adjacent their adjoining edges, said stiff member having a driving point located between the center of the diaphragm and said weight and adapted to be connected to a piezo-electric crystal, whereby during vibration of the diaphragm the part of said sealing member at the side of the diaphragm opposite said weight has a greater amplitude of vibration than said weight.

5. A sound transmitting substantially circular vibratable diaphragm for use in a case containing a piezo-electric crystal, said diaphragm comprising a relatively stifl.r conical member positioned eccentrically of the diaphragm, a resilient tab projecting laterally therefrom, and a flexible sealing member surrounding said conical member and secured thereto, the apex of said conical member being located between the center of the diaphragm and said tab and being adapted to be operatively connected to a piezo-electric crystal, andthe outer edge of said sealing member and the outer end of said tab being adapted to be restrained from vibrating when the rest of the diaphragm vibrates, whereby during vibration of the diaphragm the wide part of said sealing member farthest from said tab has a greater amplitude of vibration than said tab and the adjacent narrow part of the sealing member.

6. A soundtransmitting substantially circular vibratable diaphragm for use in a case containing a piezo-electric crystal, said diaphragm comprising a relatively stiff conical member positioned eccentrically of the diaphragm, a flexible sealing member surrounding said conical member and secured to the edge thereof, the outer edge of said sealing member being adapted `to be restrained from vibrating when the rest of the diaphragm vibrates, and a Weight attached to said conical member adjacent its edge, the apex of said conical member being located between the center of the diaphragm and said weight and being adapted to be operatively connected to a piezo-electric crystal, whereby during vibration of the diaphragm the wide part of said sealing member farthest from said weight has a greater amplitude oi.' vibration than said weight and the adjacent narrow part of the sealing member.

SAMUEL F. LYBARGER. 

